The present invention relates generally to a flow control valve and, more particularly, to a valve for maintaining the fluid flow rate in a first line at least proportional to the fluid flow rate in a second line.
The present invention will be described herein as being a part of a gasoline station vapor recovery system. However, it will be appreciated that the invention may find numerous applications, whatever it is necessary to maintain the rate of flow of fluid in one line at least proportional to the rate of flow of fluid in another line. The valve may be utilized for controlling the flows of two liquids, two gases, or a gas and a liquid.
Recent Federal regulations require that gasoline stations be provided with vapor recovery systems. In such a system, gasoline vapor collected in an automobile gasoline tank, during filling of the tank with gasoline, is drawn therefrom through a suction line into the gasoline dispensing unit or pump. A blower (pump) conveys the vapor from the unit to a condenser, where it is condensed and the condensate is returned to a gasoline storage tank. The purpose of such vapor recovery system is to minimize the escape of gasoline vapors into the atmosphere and, hence, prevent consequent air pollution.
It is desirable that a flow control valve be employed in the vapor line of the vapor recovery system which will control the flow of vapor from the automobile gasoline tank at least proportional to the flow of gasoline into the tank. At the present time, this is accomplished by the use of either two solenoid valves or a single solenoid valve combined with a flow responsive switch. Because the valves are electrically operated, they must be explosion-proof, which adds considerably to their cost. Also, the solenoid valves do not inherently modulate. Thus, it has been necessary to electrically modulate the solenoid valves to obtain the appropriate control function. Such modulation, however, considerably shortens the life of the solenoid valves, and is difficult to attain with any reasonable precision.
Therefore, what is needed and constitutes the principal object of the present invention is an improved flow control valve for use in a gasoline station vapor recovery system or the like. The valve should be simple in construction, automatically modulate or switch, and not require electrically controlled solenoids or switches which add to the expense of presently known flow control valves.